Nowadays, LCDs are widely used as flat panel displays in various appliances ranging from cellular phones to large-screen television monitors. However, since LCDs are not self-illuminating, they suffer from narrow viewing angles, and require a light source such as a backlight, which makes it impossible to reduce power consumption beyond a certain limit. To avoid these inconveniences, as alternatives to LCDs, self-illuminating display devices exploiting, for example, organic electroluminescence (hereinafter referred to as organic EL) are being studied.
This type of display device has, as pixels, organic EL elements arranged in a matrix-like pattern, and achieves image display by driving those organic EL elements to emit light individually. In a case where they are driven by an active matrix method, a thin-film transistor (hereinafter referred to as TFT) is formed in each pixel so that each pixel can be driven independently. This makes it possible to obtain high-definition, high-brightness display. In addition, it is also possible to obtain high-efficient light emission characteristics and thereby reduce power consumption. In this type of display device, for each pixel, there are provided an organic EL element that is composed of a light-emitting layer sandwiched between two electrodes, a drive TFT that feeds a current to one of the electrodes of the organic EL element, and a control TFT that controls the operation of the drive TFT. Typically, these drive and control TFTs are formed as polysilicon TFTs having a polycrystalline active layer.
Inconveniently, however, with the drive and control TFTs formed as polysilicon TFTs, the display device needs to be fabricated through a complicated, difficult fabrication process, and requires sophisticated fabrication technology and expensive fabrication equipment. This makes the display device as an end product accordingly expensive. Moreover, since it is difficult to make the active layer uniformly polycrystalline, it is difficult to fabricate large-area TFTs with uniform characteristics. This makes it difficult to fabricate a large-screen display device.